1. Field of the Invention
This invention generally relates to a composite structure formation method based on the aerosol deposition method by which an aerosol with fine particles of a brittle material dispersed in a gas is sprayed onto a substrate to form a structure made of the fine particles on the substrate, a controlled particle for use therein, and a composite structure formation system.
2. Description of the Related Art
The “aerosol deposition method” is one of the methods for forming a structure made of a brittle material on the surface of a substrate (see, e.g., Japanese Patent No. 3348154, JP-A-2006-200013(Kokai), and JP-A-2006-233334(Kokai)). In this method, an aerosol in which fine particles including a brittle material are dispersed in a gas is sprayed from a discharge port toward the substrate to collide the fine particles with the metal, glass, ceramic, or plastic substrate, deforming or fracturing the brittle material fine particles by the impact of this collision to join them together, so that a film-like structure made of the fine particles is directly formed on the substrate. This method can form a film-like structure at normal temperature without requiring any specific heating means and the like, and can provide a film-like structure having a mechanical strength which is at least comparable to that of a sintered body. Furthermore, the condition for colliding the fine particles as well as the shape, composition and the like of the fine particles can be controlled to diversely vary the density, mechanical strength, electrical characteristics and the like of the structure.
To form a large-area film-like structure by this aerosol deposition method, fine particles need to be continuously supplied for a prescribed period of time. In particular, in the case where a high film thickness accuracy is required, it is desired that the supply quantity of fine particles be constantly stable.
However, as disclosed in Japanese Patent No. 3348154, if aerosolation occurs in a storage mechanism which stores fine particles of a raw material, the fine particles stored in the storage mechanism may change the state over time, leaving a problem with stable supply of the aerosol. Furthermore, the capacity of the storage mechanism needs to be far larger than the volume of fine particles to secure the capacity for aerosolation, which may require a large-scale apparatus.
In this context, in the technique proposed in JP-A-2006-200013(Kokai), the storage mechanism for storing fine particles is separated from the aerosolation mechanism for mixing the fine particles with a gas to produce an aerosol, and the fine particles are supplied from the storage mechanism to the aerosolation mechanism by required amount.
However, in the case where submicron or smaller fine particles are used as primary particles, because of their high viscosity and adhesiveness, the problems of adhesion, stacking and the like to the wall surface are likely to occur inside the storage mechanism and in the process of supply from the storage mechanism to the aerosolation mechanism, which may make it difficult to supply reliably. For example, fine particles are likely to aggregate due to agitation and migration inside the storage mechanism and change their fluidity. Eventually, stacking occurs inside the storage mechanism and prevents migration of powder to the aerosolation mechanism, which may lose the constancy of the supply quantity. Furthermore, adhesion occurring inside the storage mechanism may also yield adverse effects, such as failing to achieve powder usage as planned.
In this regard, in the technique proposed in JP-A-2006-233334(Kokai), a split supply mechanism for supplying fine particles from the storage mechanism to the aerosolation mechanism is provided, and the fine particles stored in the storage mechanism are split into a plurality of groups and supplied by the split supply mechanism.
However, the following problems may occur in the case where a batch of brittle material fine particle powder stored in the storage mechanism is split into a plurality of groups and supplied by the split supply mechanism. Originally, the brittle material fine particle powder stored in the storage mechanism is not controlled in density and lacks uniformity in fluidity. Accordingly, the group of fine particles split in a prescribed size and shape may be nonuniform in shape and density when supplied from the storage mechanism. In some cases, the trouble of stacking of brittle material fine particle powder occurs in the storage mechanism. In such cases, even using an aerosolation mechanism having a prescribed disaggregation capability, it is difficult to generate an aerosol with a constantly stable fine particle concentration. Furthermore, if the group of fine particles split in a prescribed size and shape changes in shape or density during the supply process, it may be also difficult to accurately control the fine particle concentration in the aerosol. Moreover, at low density, the shape may collapse during the supply and cause fine particles to adhere to the inner wall of the apparatus, impairing constancy of quantity.    Patent Document: Japanese Patent No. 3348154    Patent Document: JP-A-2006-200013 (Kokai)    Patent Document: JP-A-2006-233334 (Kokai)